Paving machines are generally used for laying a heated paving material, such as bituminous aggregate mixtures or asphalt, onto a roadbed and spreading the heated paving material to achieve a road with a uniform, smooth surface. After the heated asphalt is laid it is compacted and cools so that the road becomes passable by vehicles.
The paving machines include a screed assembly for spreading the heated material. The screed assembly has one or more screed plates, and these screed plates are at times heated for ease in manipulating the heated paving material. The temperature of the screed plates is important, because if the temperature is too high, the screed may warp or the heated paving material may be damaged. Also, if the temperature is too low, the heated paving material adheres to the screed and is difficult to spread and compact. Generally, the screed plates should be heated to a temperature close to the temperature of the heated asphalt material.
Controllers have been developed for controlling the temperature of the screed plates. Published patent application WO 00/47822 is directed to a heating control system that automatically regulates the screed plate temperature by adjusting current flow through resistive heating elements for each of the screed plates. However, when the temperature of a screed plate drops below a predetermined value, the entire screed plate is heated even though only a section of the screed plate may require heating. In addition, several screed plates may be heated simultaneously. Heating the entire screed plate or several screed plates simultaneously drains the power supply, which is used for other functions, such as lighting, of the paving machine, and such general heating is inefficient.
The present invention is directed to overcome one or more of the problems as set forth above.